As everyone said bitcoin doesn't require approval from any country to be used by its people. Citizens of any country can buy and sell bitcoins as long as they have internet. But it could be called as illegal activity if your country has banned bitcoin.
If bitcoin is illegal in your country it is better to avoid trouble and to not use bitcoin or other cryptocurrencies, governments are very bipolar some of the countries that banned cryptocurrencies will change their mind in the future as some countries already did in the past, they are going to realize that trying to stop bitcoin is an useless endeavor and they will instead dedicate their time to try to regulate the market.